Thallus to 5-7 cm diam., often smaller, level with or sunken into the substratum. Lobes 5-10 mm wide [sometimes broader in Scandinavian material], to 35 mm long, concave to ear-shaped, with ascending, entire or ± eroded, thickened and sometimes inrolled margins. Upper surface grey-brown to olive brown (rarely olive green in fully hydrated conditions), smooth, glabrous in part or ± thinly tomentose to somewhat scabrous. Isidia to 1.5 mm diam., numerous, button-like, resembling cephalodia, crowded and contiguous, sometimes overlapping or widely dispersed. Lower surface pale, with often rather indistinct white to pale grey, rarely pale brown anastomosing veins and discrete to confluent unbranched pale to brown rhizines. Photobiont cyanobacteria (Nostoc).
Anamorph: not known.
Teleomorph: ascomata apothecia, not known in the British Isles; on shortly elongate lobes, the disc 3-7 mm diam., saddle-shaped. Ascospores 49-59 x ca 5 µm.
Chemistry: thallus with no positive reactions. No lichen products detected by TLC.
Assessed as Critically Endangered (B) by Woods & Coppins (2012). It is considered to be Nationally Rare, and is a (former) BAP Priority Species listed under Section 2(4) of the Nature Conservation (Scotland) Act 2004.
Distinguished by the small size and numerous dorsiventral peltate cephalodia-like isidia on the partly thinly tomentose upper surface. It is rather similar to young thalli of the widespread species Peltigera didactyla, which becomes sorediate with age.
Only known from a single site in VC89 East Perthshire, last observed there in 2004.
On flat mossy rock ledges in a river gorge.